Phonograph pick-up



April 14, 1936. A. cRossLEY ET AL v 2,037,639

PHONOGRAPH P I CK -UP Filed June 27, 1950 2 Sheets-Sheet, 1

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PHONQGRAPH' PICK-UP Filed June 27, 195oA 2 sheets-sheet 2 jvennst Patented Apr. 14, 1936 UNITED STATES PATEN'I" OFFICE PHONOGRAPH PICK-UP of Delaware Application June 27, 1930, Serial No. 464,410

Claims.

This invention relates to improvements in phonograph pickup mechanism and,'more especially, such mechanism adapted for use with a radio receiver whereby phonographic records may be reproduced through the loud speaker or phones of a radio receiver.

Our mechanism includes a pickup transformer, the secondary coil of which is connected to the grid of the detector tube; and means are provided for automatically changing the value of the bias resistor of this tube when the pickup mechanism is turned on, or cut in, so that the detector tube will operate on the straight portion of its curve in reproducing the phonograph record, thus giving true amplification.

Another feature of our invention is the provision of means for vautomatically short circuiting the secondary coil of the last radio frequency transformer of the receiver when the pickup is turned on, thus eliminating or lessening the possibility of undesirable radio signals coming through to the detector tube and interfering with the phonograph record reproduction.

Another feature of our invention is the provision of means requiring the radio receiver tuning mechanism to be moved to the limit of its operating range before the phonograph pickup can be turned on. This causes complete detuning of the receiver or setting o-f it outside of the usual broadcast band thus further lessening or eliminating interference from radio broadcast signals.

Another feature of our invention is the provision of means for automatically turning on or cutting in the phonograph pickup by movement of the radio receiver tuning mechanism to the limit of its operating range.

Other features and advantages of our invention will appear more fully as we proceed with our specification.

In that form of device embodying the features of our invention shown in the accompanying drawings, Fig. 1 is a View in front elevation of a radio receiver showing the tuning mechanism and its connection to the pickup switch, Fig. 2 is an enlarged detail view of such connection with the pickup switch in its .on position, Fig. 3 is a similar View with the switch in its olf position, Fig. 4 is a View taken as indicated by the line 4 of Fig. 1, Fig. 5 is a detail view of the phonograph pickup switch showing the same in its off position, and Fig. 6 is a schematic wirreceiver. Our invention may be used with practically any form of such-receiver. We shall refer only to portions of the same in explaining our invention; it being understood that there may be embodied in the receiver such radio frequency and audio frequency amplifying means and other details of radio receiver design as may be desired.

In the accompanying drawings, I0 may indicate, in general, the chassis of a radio receiver. Purely for purposes of illustration this receiver is shown With tuning mechanism for simultaneously rotating the shafts I I, I2, I3 and I4 which, for example, may be the shafts of a plurality or gang of condensers (not fully shown). The details of this tuning mechanism which is shown and claimed in a co-pending application need not be described in detail here as they form no part of the present invention. It will sufce to say that the operating knob I5 rotates a friction disk (not shown) which rotates the disk I6 on the shaft I3. Rotation of the shaft I3 is imparted to the shafts I I, I2, and I4 by means of belt wheels I'I and belts I8 connecting the same. The setting of the tuning mechanism is indicated by a calibrated scale I9 that is reciprocated by a cord 20 wound about a groove in the periphery of the disk I6 with its ends passing over the pulleys 2I and attached to the ends of the scale I9 at 26a.

It will aid in the description to refer next to the wiring diagram shown in Fig. 6. As here shown, 25 may indicate the usual detector tube of the receiver, and 26, its bias resistor when it operates as a radio detector tube. In accordance with well-known practice, the valve of this resistor is such as to cause the tube to operate on the curved portion of its curve when detecting radio signals. When it is desired to use such tube for amplifying phonograph pickup signals, it is desirable to change its bias voltage to operate the same on the straight portion of its curve so as to give true amplification. This can be accomplished by changing the value of the resistor, usually by decreasing the amount of such resistance. We accomplish this by providing an additional resistor 2'I which is automatically shunted across the resistor 26 when the pickup is turned on. This shunting is effected by closing the switch 28. When switch 28 is open, as shown by the solid lines in Fig. 6, only resistor 26 is connected between the cathode 29 of the detector tube and ground 30. When switch 28 is closed, as shown by the broken lines in Fig. 6, resistor 21 is also connected between the cathode and ground. v

In order to lessen or eliminate the possibility of radio signals coming through to the detector tube when the pickup is being used, we provide also the switch 3l which short circuits (as shown by broken lines in Fig. 6) the secondary coil 32a of the last radio frequency transformer 32 when the pickup is turned on. When the pickup is not being used, this switch is in the position shown by the solid lines (in Fig. 6) with the coil 32a connected to the detector tube for usual radio receiving. In this position, the secondary of 33 is short circuited, thus providing a short path to ground. It is to be understood that following or connected to the detector tube there may be employed the usual audio frequency transformer 6B, and any desired audio frequency amplifying means, loud speakers, telephones, or the like, for amplifying or reproducing radio signals or phonograph record signals. Numeral 33 indicates the usual pickup transformer and 34, the wires leading to the pickup (not shown).

The mechanical details of the switches 28 and 3l are shown in Figs. 4 and 5. Both of these switches are operated by rotation of the shaft 4l which carries a cam 42. The cam is preferably made of bakelite, while arm 45 is riveted to the cam and insulated from shaft 4I.

The spring arm 36 lies against a flat place 1&2a on the cam 42 when the switch is olf or in the position shown in Fig. 5, i. e., adjusted for radio reception (or by the solid lines in Fig. 6). When in this position, the arm 36, which is connected to ground 3Q by wire 36e, is out of contact with point 35 connected to resistor 21 by wire 352L and the two projections 55, 45 carried by the cam 42 electrically connect the terminals 33 and 39.

When the pickup is turned on, the shaft 4l is rotated to cause the cam 42 to press the spring arm 35 into contact with the point 35 and move the arms d5, 135, to break contact between the terminals 38 and 39 and make contact between the terminals 3l and d. The parts are shown in these positions by the broken lines in Fig. 6.

Rotation of the shaft 4l to turn the pickup on or "off is accomplished in the following manner. The end of the shaft carries a crank disk 5D provided with a crank pin 5I embraced by a slot 52 in the end of the lever 53 pivotally mounted at 54. The other end of the lever 53 is provided with a slot 55 embracing (except as hereinafter noted) the pin 56 on one of the wheels l1 forming a part of the tuning mechanism above described. The parts are so arranged that as the tuning mechanism is operated to the limit of its operating range, the pin 56 will enter the slot 55 and turn on the pickup.

In Fig. 3, the parts are shown with the wheel I'l being turned in the direction indicated by the arrow. The receiver has just been detuned (for example, above the broadcast range), but the pickup switch is still off. A slight further rotation in the direction indicated by the arrow will rock the lever 53 to turn on the pickup switch and the tuning mechanism will then be at the limit of its travel. The parts are shown in this position in Fig. 2. Reverse movement of the tuning mechanism will rock the lever 53 into the position shown in Fig, 3, thus turning off the pickup, and the pin 55 will then be permitted to leave the slot 55 (the lower side being cut away, as indicated by 55a for this purpose) to permit the normal use of the tuning mechanism in its operating range for the reception of radio signals.

While we have shown and described certain embodiments of our invention, it is to be noted that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims, in which it is our intention to claim all novelty inherent in our invention as broadly as permissible, in View of the prior art.

What we regard as new, and desire to secure by Letters Patent, is:

1. In a radio phonograph combination, a detector tube of the negative grid bias type, means for supplying radio frequency energy to said detector tube, means for supplying audio frequency energy to said detector tube, means for shortcircuiting each of the last mentioned means when the other means thereof is being used, and means for decreasing the negative bias of said detector tube when the means for supplying radio frequency energy to said tube is short-circuited.

2. In a radio receiving apparatus, the combination with an electron discharge device having at least a cathode and a control grid, of two seriesconnected windings connected between said grid and cathode, a source of radio frequency energy coupled to one of said windings, a source of audio frequency energy coupled to the other of said windings, and switching mechanism so interconnecting said windings that in one position of said mechanism one of said windings is shortcircuited and in a second position the other of said windings is short-circuited and simultaneously a resistance is connected between cathode and the grid return, in either of said positions the winding that is not short-circuited being operatively connected to the grid and cathode electrodes.

3. In a radio receiving apparatus, the combination with an electron discharge device having at least a cathode and a control grid, of two series-connected windings connected between said grid and cathode, a source of radio frequency energy coupled to one of said windings, a source of audio frequency energy coupled to the other of said windings, and switching mechanism so interconnecting said windings that in one position of said mechanism one of said windings is short-circuited and simultaneously a condenser is shunted across the other winding, and in a second position said other winding is short-circuited and simultaneously a resistance is connected between cathode and the grid return, in either of said positions the winding that is not short-circuited being operatively connected to the grid and cathode electrodes.

4. In a radio receiving apparatus, the combination with an electron discharge device having at least a cathode and a control grid, of a cathode biasing resistor, two series-connected windings connected between said grid and the low potential side of the cathode resistor, a source of radio frequency energy coupled to one of said windings, a source of audio frequency energy coupled to the other of said windings, and switching mechanism so interconnecting said windings that in one position of said mechanism one of said windings is short-circuited and simultaneously a variable tuning condenser is shunted across the other winding, and in a second position said other winding is short-circuited and simultaneously a resistance is shunted across the cathode biasing resistor, in either of said positions the winding that is not short-circuited being operatively connected to the grid and cathode electrodes.

5. In a radio receiving apparatus, the combination with an electron discharge device having at least a cathode and a control grid, of a cathode biasing resistor, two series-connected windings connected between said grid and the low potential side of the cathode resistor, a source of radio frequency energy coupled to one of said windings, a source of audio frequency energy coupled to the other of said windings, and switching mechanism so interconnecting said windings that in one position of said mechanism one of said windings is short-circuited and simultaneously a variable tuning condenser is shunted across the other winding, and in a second position said other winding is short-circuited and simultaneously a resistance is shunted across the cathode biasing resistor, in eitherof said positions the winding that is not short-circuited being operatively connected to the grid and cathode electrodes, said switching mechanism being thrown to the second mentioned position when said variable tuning condenser is adjusted to one of its two limits of travel.

ALFRED CROSSLEY.

LELAND H. HANSEN. 

